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903 cummins thermostat
#1

When I brought the coach home last fall it was running cool on the interstate (140-160); seems like it needs a thermostat.
Now that the outside temperature is finally above freezing I'm able to do some work on it. I have a thermostat, but I can't seem to find where it goes.
Both upper radiator hoses and the lower have housings that don't seem to be the right size. Nothing else looks obvious either.
Can someone point me in the right direction?
We're leaving for spring break in 2 weeks, the pressure is on now.

Thanks

Scott

1983 38' Classic #007
8.3 Cummins, Allison 6 spd.
"Any other Way"
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#2

dean s. didnt you have a 903? can you help scott out?

tom

2002 45'8" Newell Coach 608  Series 60 DDEC4/Allison World 6 Speed HD4000MH

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#3

I had the 555 which is similar. Generally the thermostat will install between the upper radiator hose and the engine. Your 903 may have a thermostat in each hose. It will mount inside the housing that bolts to the head. An engine manual would show exactly where. Manuals are a good investment and can be bought on ebay. While you have the system apart you should drain and replace the coolant if you don't know when it was last changed. These engines have "wet" cylinder liners that are subject to coolant cavitation corrosion. A cavitation inhibitor MUST be added to the coolant. Cooling system failures are one of the most common causes of engine failure.

1993 Newell (316) 45' 8V92,towing an Imperial open trailer or RnR custom built enclosed trailer. FMCA#232958 '67 Airstream Overlander 27' '67GTO,'76TransAm,'52Chevy panel, 2000 Corvette "Lingenfelter"modified, '23 Grand Cherokee.
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#4

I finally got both thermostats out last night, weird two piece housing design under the upper hoses.
I suspect the problem is leakage past the seals, the thermostats seemed to work when I tested them. Both new thermostats and seals will go in after I get the cast iron housings cleaned up and painted.
I bought several bottles of additive and test strips a few weeks ago. I tested it coming out, a little low in moly, the nitrates were good. Good to know what was in there recently was good, I hope it's been so for the previous 30 years.

Scott

1983 38' Classic #007
8.3 Cummins, Allison 6 spd.
"Any other Way"
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